Low Temperature Preservation: Chilling and Freezing Techniques

Meat is one of the most perishable food products. The moment an animal is slaughtered, a race against time begins – enzymes start breaking down muscle tissue, and bacteria begin to multiply on the surface. Low temperature preservation is the primary defence against this spoilage. By using chilling and freezing, the meat industry can dramatically slow microbial growth and enzymatic activity, keeping meat safe, nutritious, and flavourful for days, weeks, or even months.

Why does low temperature work? 🔗

Microorganisms need warmth, moisture, and nutrients to thrive. Meat, being rich in proteins, lipids, and water, is an ideal growth medium for bacteria. Lowering the temperature reduces the kinetic energy of molecules inside the meat, which in turn slows down both microbial multiplication and the chemical reactions (like oxidation and proteolysis) that cause spoilage. The colder the environment, the slower these processes become – until, at freezing temperatures, most biological activity effectively stops.

It is important to note that low temperatures do not kill most bacteria. They simply put microorganisms into a dormant or very slow-growing state. Once the meat is brought back to warmer temperatures, surviving bacteria can resume multiplying. This is why maintaining an unbroken cold chain – from slaughterhouse to consumer’s kitchen – is absolutely critical for meat safety.

Chilling: the first line of defence 🔗

Chilling refers to reducing and maintaining the temperature of meat just above its freezing point, typically in the range of 0°C to 4°C. It is the most widely used short-term preservation method for fresh meat. The goal is to bring the surface temperature down quickly after slaughter so that bacteria do not get a head start.

Primary chilling after slaughter 🔗

Immediately after dressing, carcasses are placed in cold chambers where chilled air at around 0°C is circulated at speeds of 0.75 to 1.5 m/s. The aim is to bring the surface temperature to near 0°C within the first four hours and the core temperature of the carcass to about 7°C within 16-24 hours for small carcasses, or up to 48 hours for large ones like beef hindquarters. Relative humidity in the chilling room is kept high – between 90% and 95% – to minimize weight loss from surface evaporation.

Speed matters here. The faster the surface cools, the less opportunity bacteria have to multiply. However, cooling too aggressively carries its own risk: a phenomenon called cold shortening. This occurs when pre-rigor meat (meat that has not yet completed rigor mortis) is cooled below 10°C too quickly, causing the muscle fibres to contract irreversibly, resulting in tough meat even after prolonged ageing.

Chilled storage conditions 🔗

Once primary chilling is complete, meat enters chilled storage. During this phase, ageing (or ripening) also takes place – natural enzymes slowly break down connective tissue, making the meat more tender and flavourful. Ageing requirements vary by species: poultry needs only a few hours, pork takes two to four days, mutton about four days, and beef can take up to two weeks at around 4°C.

For longer chilled storage, a temperature close to 0°C is preferred, with relative humidity of 80-90%. Under these conditions, fresh beef can be stored for three to five weeks, while pork and poultry have shorter shelf lives of one to two weeks. Proper air circulation – typically 20 to 35 air changes per hour – and correct spacing of carcasses help maintain uniform conditions throughout the cold room.

Freezing: long-term preservation 🔗

When meat needs to be preserved for weeks or months – for buffer stock, export, or later processing – freezing is the method of choice. Freezing works by lowering meat temperature to -18°C or below, converting most of the water inside the tissue into ice crystals. This achieves two things simultaneously: it halts microbial growth almost completely, and it dramatically reduces the water activity of the product, making conditions inhospitable for any surviving organisms.

Meat is typically considered fully frozen when its centre reaches -12°C or lower. At -18°C – the internationally recommended storage temperature – about 80% of the water in the meat has turned to ice. Even at very low temperatures like -60°C, a small fraction of water remains unfrozen due to the increasing concentration of dissolved solutes as ice forms.

Slow freezing vs. quick freezing 🔗

The rate at which meat freezes has a significant impact on final product quality. This is because freezing rate determines the size and location of the ice crystals that form within the tissue.

Slow freezing (below 1 cm/h through the product) allows water to migrate out of the muscle cells before crystallizing. The result is fewer but larger ice crystals, primarily formed in the spaces between cells. These large crystals can physically damage cell walls, and when the meat is later thawed, a significant amount of moisture – called drip loss – escapes from the ruptured cells. This leads to a drier, less tender product with reduced juiciness.

Quick freezing (above 5 cm/h) produces many small ice crystals distributed evenly both inside and outside the muscle cells. Because these tiny crystals cause minimal mechanical damage to the cellular structure, quick-frozen meat retains much more of its original texture, colour, and juiciness upon thawing. The International Institute of Refrigeration (IIR) recommends a freezing front velocity of 2 to 5 cm/h for good quality results.

Commercial freezing methods 🔗

The meat industry uses several types of industrial freezers, each suited to different products and production volumes. The choice depends on factors like the shape and size of the product, required throughput, energy costs, and desired quality.

Air blast freezing 🔗

This is one of the most common commercial freezing methods. Powerful fans circulate pre-cooled air at temperatures of -30°C to -40°C over the meat products at speeds of 1.5 to 6 m/s. The high-velocity airflow strips away the insulating boundary layer of air around the product, enabling much faster heat removal than a standard storage freezer. Depending on product size, blast freezing can reduce freezing times to between 30 minutes and a few hours.

Blast freezers come in different configurations. Tunnel freezers move products through a freezing zone on a conveyor belt, making them ideal for continuous, high-volume operations. Batch blast freezers hold a fixed quantity of product and are suited for smaller operations. Spiral freezers use a compact, spiralling conveyor belt to achieve high throughput in a smaller footprint.

Plate freezing 🔗

In plate freezers, meat is placed between hollow metal plates through which a refrigerant circulates. The direct contact between the cold plate surface and the meat provides highly efficient heat transfer. This method works best for flat, uniformly shaped products like fish fillets, beef patties, boneless cuts, and packaged blocks of meat. Plate freezing is energy-efficient and produces well-shaped blocks that are easy to stack and store. However, it is not suitable for irregularly shaped items like whole carcasses or bone-in cuts.

Cryogenic freezing 🔗

Cryogenic freezing uses ultra-cold liquefied gases – typically liquid nitrogen at -196°C or liquid carbon dioxide at -78°C – in direct contact with the meat product. This is the fastest freezing method available commercially, capable of freezing products in minutes rather than hours. The ultra-rapid cooling produces extremely small ice crystals, preserving cellular structure and minimising drip loss upon thawing.

Because of its speed and superior quality retention, cryogenic freezing is often used for high-value products like premium meat cuts, seafood, and individually quick-frozen (IQF) items. The trade-off is cost – while the initial equipment investment may be relatively low, the ongoing expense of purchasing liquefied gases makes this method significantly more expensive to operate than air blast or plate systems.

Immersion freezing 🔗

In immersion freezing, meat products are submerged in a chilled liquid, such as brine, glycol, or calcium chloride solution. Because liquids transfer heat much more efficiently than air, this method achieves rapid and uniform freezing. It is particularly popular for whole poultry, where the liquid can surround the entire surface of the bird, including body cavities. The product may be in direct contact with the liquid or separated by a flexible packaging membrane to prevent flavour transfer.

Factors affecting frozen meat quality 🔗

Even after meat is properly frozen, several factors determine how well its quality is maintained over time.

Storage temperature 🔗

The recommended storage temperature for frozen meat is -18°C or below. At this temperature, microbial growth is effectively halted and enzymatic activity is extremely slow. Storing meat at warmer sub-zero temperatures (say -5°C to -10°C) does not stop spoilage entirely – yeasts and moulds that are both cold-tolerant and adapted to low water activity can still grow under these conditions.

Temperature fluctuations 🔗

Inconsistent storage temperatures are one of the biggest enemies of frozen meat quality. When temperature rises temporarily, some ice crystals melt. When the temperature drops again, the water refreezes into larger crystals. This repeated cycle of partial thawing and refreezing – known as recrystallisation – progressively damages cell structure, increases drip loss, and degrades texture over time.

Packaging and freezer burn 🔗

Freezer burn occurs when frozen meat loses moisture through surface sublimation – ice transitions directly into water vapour without melting first, leaving behind dry, discoloured patches. According to Penn State Extension, vacuum-sealing is the most effective way to minimise air exposure and protect against freezer burn. Meat packaged in standard wrapping is far more susceptible to dehydration and quality loss during extended storage.

Thawing practices 🔗

How meat is thawed also influences final quality. The safest and most quality-preserving method is slow thawing in the refrigerator at 4°C or below, allowing the meat to gradually reabsorb moisture released during ice crystal melting. Thawing at room temperature creates a situation where the outer surface warms into the danger zone (4°C-60°C) while the interior is still frozen, promoting bacterial growth on the surface. Microwave thawing is an option for speed but should be followed immediately by cooking.

Shelf life of frozen meat 🔗

When stored at a constant -18°C in proper packaging, different types of meat have varying recommended storage times. Beef and lamb generally maintain good quality for up to 12 months. Pork has a somewhat shorter recommended shelf life of around 6 to 8 months, partly because its higher fat content makes it more susceptible to oxidative rancidity. Poultry can be stored for 9 to 12 months, while ground meat and cured products like bacon and ham are best used within 1 to 3 months due to accelerated rancidity from salt and increased surface area. As noted by the National Center for Home Food Preservation, cured meats in particular have a limited freezer life because salt speeds up fat oxidation.

It is worth noting that properly frozen meat remains safe indefinitely – the storage time recommendations are about quality (taste, texture, appearance), not safety. Meat stored at 0°F (-18°C) will not support pathogenic bacterial growth regardless of how long it is stored.

Practical significance of low temperature preservation 🔗

Low temperature preservation is not just a technical process – it has wide-ranging implications for the entire meat supply chain. Chilling enables the short-distance distribution of fresh meat while maintaining quality consumers expect. Freezing makes it possible to build buffer stocks, manage seasonal demand fluctuations, and transport meat across long distances and international borders without spoilage.

For developing countries with limited cold chain infrastructure, improving access to reliable chilling and freezing facilities can make a substantial difference in reducing post-harvest meat losses and improving food security. In countries like India, where a significant portion of meat can be lost to spoilage between the slaughterhouse and the consumer, investment in cold chain technology is directly linked to reduced food waste and better nutrition outcomes.

What do you think? Given the clear advantages of quick freezing over slow freezing, why do you think many small-scale meat processors still rely on conventional slow-freezing methods? How might affordable cold chain solutions reshape meat distribution in developing regions?

References

1. https://www.fao.org/4/t0098e/t0098e02.htm
2. https://www.fao.org/4/y5979e/y5979e03.htm
3. https://www.britannica.com/topic/food-preservation/Industrial-freezers
4. https://www.foodengineeringmag.com/articles/100699-tech-update-freezing-and-cooling
5. https://extension.psu.edu/freezing-and-refreezing-meat
6. https://nchfp.uga.edu/how/freeze/meat-and-poultry-products/freezing-meats/